Technical Field
The present invention relates to a sealing member for a fuel cell to be used for sealing a constituent member of a fuel cell such as a metal separator. More particularly, the present invention relates to a sealing member for a fuel cell exhibiting an excellent low-temperature sealing property and a fuel cell sealed body using the same.
Background Art
Fuel cells, which generate electricity through an electrochemical reaction of gases, exhibit high power generation efficiency, and have an extremely small influence on the environment by virtue of discharging a clean gas. Of the fuel cells, a polymer electrolyte fuel cell can be operated at relatively low temperature and has a high power density. Therefore, the polymer electrolyte fuel cell is expected to be used in various applications such as a power source for power generation and a power source for an automobile.
The polymer electrolyte fuel cell includes as a power generation unit a cell including metal separators and a membrane electrode assembly (MEA) or the like sandwiched between the metal separators. The MEA is formed of a polymer membrane (electrolyte membrane) serving as an electrolyte and a pair of electrode catalyst layers [a fuel electrode (anode) catalyst layer and an oxygen electrode (cathode) catalyst layer] arranged on both surfaces of the electrolyte membrane in its thickness direction. Further, a porous layer (gas diffusion layer) for diffusing a gas is arranged on each of surfaces of the pair of electrode catalyst layers. A fuel gas such as hydrogen is supplied to a fuel electrode side, and an oxidant gas such as oxygen or air is supplied to an oxygen electrode side. Power is generated through an electrochemical reaction at a three-phase interface between the supplied gas, the electrolyte, and the electrode catalyst layer. The polymer electrolyte fuel cell is constructed by securing a cell stack, in which a plurality of the cells are stacked, with end plates or the like arranged at both ends of the cell stack in a cell stacking direction.
In addition, the metal separators each include a flow passage for the gas to be supplied to each of the electrodes and a flow passage for a cooling medium for alleviating heat to be generated during the power generation. In addition, it is necessary to keep the electrolyte membrane in a wet state at the time of operation, because the electrolyte membrane exhibits proton conductivity in a state of containing water. Therefore, in order to prevent the gases from being mixed with each other, prevent leakage of the gases and cooling medium, and keep an inside of the cell in a wet state, it is important to ensure a sealing property at a periphery of the MEA and porous layers or a sealing property between the metal separators adjacent to each other. As a sealing member for sealing such constituent member, there has been proposed, for example, an adhesive sealing member for a fuel cell that ensures a sealing property with the constituent member such as a metal separator without applying an adhesive agent (free of an adhesive agent) by kneading an adhesive component such as a resorcinol-based compound into a rubber component such as an ethylene-propylene rubber (EPM) or an ethylene-propylene-diene rubber (EPDM) and thereby allowing the sealing member itself to have adhesiveness (see JP-A-2011-249283). Further, such sealing member has a risk of losing rubber elasticity of the EPM or EPDM at extremely low temperature, and hence it is difficult to ensure a desired sealing property in the case of using a fuel cell in cold climates or the like. Accordingly, there have been investigations on development of a sealing member capable of exhibiting a satisfactory sealing property even at extremely low temperature. For example, there has been proposed an adhesive sealing member for a fuel cell including a rubber component formed of at least one of an EPM or EPDM having a content of ethylene of at most 53 wt %, an organic peroxide having a 1 hour half-life temperature of at most 130° C., a cross-linking aid, and a specific adhesive component (see JP-A-2012-226908).